Brainless slime mould can 'learn' to avoid icky things

Single celled organisms are not famed for their intelligence – but a new study suggests that, even without a brain, slime mould can actually "learn".

In a study published in Proceedings of the Royal Society B, a team from the Research Centre on Animal Cognition at Toulouse University outlined how slime mould can learn to avoid irritants, even without a nervous system. The team described the discovery as "tantalising" and suggested that "the hallmarks for learning can occur at the level of single cells".

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The research undertaken was "habituation learning" – essentially when behaviour changes according to a particular stimulus.

Petri dishes full of P. polycephalum cells, grown inside agar jelly, were placed near oatmeal and inside jelly. They were separated by a "bridge" of jelly, which the slime crawled across in around two hours. Two separate bridges were then contaminated with bitter concentrations of quinine and caffeine.

The slime initially hesitated, and even stopped for several hours before moving slowly across the bridge, attempting to not touch the bitter substance, to reach the food.

But after several days of trials, this time was cut down – which the team says means the slime had become habituated to the bitterness. "What's interesting about slime moulds is that they appear to be simple, but they are capable of amazing stuff," said lead author Roman Boisseau.

This includes an ability for the mould to find its way around mazes and even choosethe best diet for itself – and the team say that this study confirms that cognitive ability. "Our results point to the diversity of organisms lacking neurons, which likely display a hitherto unrecognised capacity for learning, and suggest that slime moulds may be an ideal model system in which to investigate fundamental mechanisms underlying learning processes," Boisseau added. The findings, he suggested, could help us understand when and where in the tree of life the "earliest manifestations of learning evolved".